Refrigeration systems are known for use with freezers of the type known as “ultra-low temperature freezers” (“ULT's”), which are used to cool their interior storage spaces to relative low temperatures such as about −80° C. or lower, for example.
Known refrigeration systems of this type include two stages circulating respective first and second refrigerants. The first stage transfers energy (i.e., heat) from the first refrigerant to the surrounding environment through a condenser, while the second refrigerant of the second stage receives energy from the cooled space (e.g., a cabinet interior) through an evaporator. Heat is transferred from the second refrigerant to the first refrigerant through a heat exchanger that is in fluid communication with the two stages of the refrigeration system.
In refrigeration systems of the type described above, the heat exchanger may be of a single-pass, coiled type. Heat exchangers of this type, however, typically occupy large spaces to permit the desired type of heat exchange between the refrigerants. The space and orientation requirements for these heat exchangers force designers to place them alongside or behind the walls of the inner freezer chamber, in front of the outer freezer cabinet, typically taking up valuable cooling/storage space thus not available for cooling.
In addition to the above, the attainable efficiency of these heat exchangers is limited by the relatively small amount of insulation that can be arranged around them between the walls of the inner freezer chamber and the outer freezer cabinet. Specifically, a relative small amount of insulation is placed around a heat exchanger of a refrigeration system of this type in order to minimize the amount of cooling/storage space that is lost to the heat exchanger.
There is a need, therefore, for refrigeration systems for use with ultra-low temperature freezers that can operate with a relative large efficiency, and which permit maximization of the cooling/storage space of the freezer.